This disclosure relates to a method for automatic calibration of a position detection sensor of an automatic transmission comprising a gearshift actuator. The disclosure also relates to an automatic transmission being calibrated by such a method, as well as a vehicle comprising such an automatic transmission.
This is advantageous in optimising the performance of automatic transmissions, especially for trucks, semi-trucks, road trains and the like, but may also be used in other vehicles.
Advancements in transmission technology allows for more and more effective implementations of automatic and semi-automatic transmissions in vehicles which assist in promoting more optimal operation of such vehicles. This aid in improving fuel economy, reducing the time spent accelerating or decelerating to a desired speed, and reducing fatigue in drivers who can focus on the road instead of the operation of the transmission. Automatic and semi-automatic transmissions have lately also been introduced into heavier vehicles such as trucks, semi-trucks, road trains and the like, and made feasible as a result of improvements to these transmissions.
In order for automatic transmission to be feasible in such heavy vehicles, advanced control units, often called Gearshift Control Units (GCU), which control the transmission may be necessary. To service these transmissions, the GCU may need to be removed, possibly to allow replacement of the GCU, access to the transmission or to service the GCU unit itself. Removing or replacing the SCUD is a complicated task, as it is connected to and controls the actuation of the different gears of the transmission, and in the case of vehicles which include a splitter for multiple gear levels such as e.g. a semi-truck, it also controls the actuation of the splitter. The operation of these gearshift actuators is critical to the correct operation of the automatic transmission, as they enable the GCU to change gears. The automatic transmission may be equipped with position detection sensors which are used for controlling and verifying the position of the gearshift actuators, and to ensure correct operation, the position detection sensors have to be calibrated.
JP2004084890A discloses storing the characteristics of an automatic transmission electronic control unit to prevent behavioural change of the transmission when parts are replaced, substituting the variation characteristics of the previous part with an inputted variation characteristic.
This solution involves transfer of data from one transmission electronic control unit to another control unit to ensure a similar operation of the replaced unit. However, further improvements with respect to service and repair of transmission units are desired.
It is desirable to provide a more effective method for automatic calibration of an automatic transmission.
This disclosure concerns a method for automatic calibration of a position detection sensor of an automatic transmission comprising a gearshift actuator, the method comprising registering, using the position detection sensor, the position of the gearshift actuator upon power-up of the transmission; and performing a calibration of the position detection sensor if the registered position of the gearshift actuator is outside a predetermined expected position range of the gearshift actuator or if the registered position of the gearshift actuator is within a predetermined abnormal position range of the gearshift actuator.
Each gearshift actuators of the automatic transmission is often pneumatically controlled using at least one directional control valve, which received control signals from a microprocessor of the gearshift control unit. The control signal of the microprocessor may typically correspond to two or three predetermined positions of the gearshift actuator, such as neutral, left engaged and/or right engaged. The at least one directional control valve is arranged to control the gearshift actuator accordingly, i.e. to position the gearshift actuator in a predetermined neutral, left and/or right position, which positions corresponds to different longitudinal actuating position of the gearshift actuator. The transmission further comprises position detection sensor for monitoring the actuating position of the gearshift actuators. Normally, the actuating position of each gearshift actuator is monitored by an individual position detection sensor. Upon issuing a command by the electronic control unit to move a gearshift actuator to a certain actuating position, the position detection sensors provide feedback to the electronic control unit about the time point when the desired actuation position of the gearshift actuator was attained. Any discrepancy between the commanded actuating position and actual actuating position may consequently immediately be determined.
Upon removal of the gearshift control unit and potential service or repair thereof the position detection sensors associated with the gearshift actuators may be replaced, renewed, dislocated or the like, such that the output signal of any position detection sensor no longer with certainty can be associated with any physical actuation position of the gearshift actuator. Calibration of the position detection sensors are consequently required after assembly of the transmission and gearshift control unit to certify that the output signal of each position detection sensor can be associated with a specific actuation position of the corresponding gearshift actuator.
Calibration can for example be performed by the electronic gearshift control unit by commanding the gearshift actuator to consecutively attain the different predetermined actuating positions and registering the output signal of the position detection sensor for each predetermined actuating position, such that a unique output signal can be coupled to each unique actuating position of the gearshift actuator. Alternatively, only the actuating position corresponding to the neutral position is checked.
One solution is to perform calibration of the position detection sensors at each transmission power-up for ensuring that the position detection sensors are always correctly calibrated. However, this calibration strategy tends to slow down transmission power-up and the calibration is in most circumstance unnecessary. Another calibration strategy is to manually initiate calibration after transmission service or repair but there is a risk that the service technician forgets to initiate the calibration.
With the method according to the disclosure the calibration of the position detection sensor is performed automatically when required. The basic idea of the disclosure is the fact that the gearshift actuators often exhibit a different actuating position after transmission service or repair, or when the gearshift control unit was temporarily dismounted from the transmission housing. During a normal engine shut down each gearshift actuator is controlled to exhibit a predetermined actuating position. However, the gearshift actuators often have to exhibit a different actuating position for enabling assembly of the gearshift control unit with the transmission housing. Consequently, simply be registering the output signal of the uncalibrated position detection sensors upon transmission power-up, an indication that a calibration of the position detection sensors can be determined. When the registered position of the gearshift actuator is outside a predetermined expected position range of the gearshift actuator then this is strong indication that a calibration is required. Similarly, when the registered position of the gearshift actuator is within a predetermined abnormal position range then this also is a strong indication that a calibration is required. Automatic calibration of the position detection sensors according to the disclosure improves start up times of the automatic transmission because calibration is only performed when needed, and at least not upon each transmission power-up. This calibration strategy thus improves start-up times as calibration will only be performed in certain circumstances.
This disclosure further concerns a method for automatic calibration of a position detection sensor of an automatic transmission comprising a gearshift actuator, wherein the method comprising performing a calibration of the position detection sensor associated with the gearshift actuator if, upon power-up of the transmission, a recent request for preparing the automatic transmission for disassembly can be detected.
This alternative solution for identifying an indication that a calibration of the position detection sensors is required involves an analysis of the recent command history received by the gearshift control unit. Frequently at least one of the gearshift actuators must be set in a specific actuating position for enabling the gearshift control unit to be removed from the transmission housing. The reason for this is that the shift forks of the gearshift control unit protrude out of the gearshift control unit and into the transmission housing in the assembled state. The at least one opening in the transmission housing receiving the shift forks is generally dimensioned to be as small as possible for avoiding unnecessary weakening of the structural rigidity of the transmission housing. Consequently, for being able to withdraw the shift forks out through the opening of the transmission housing at least one of the shift forks often must be set in a specific actuating position. For preparing dismounting of the gearshift control unit a specific control command is received by the gearshift control unit for preparing the transmission for disassembly. In response to this control command the gearshift control unit controls the gearshift actuators according to a predetermined pattern thereby enabling withdrawal of the gearshift control unit and shift forks without further displacement of the shift forks being necessary. The alternative solution for identifying an indication of need for calibration of the position detection sensors involves thus an analysis of the recent control commands received by the gearshift control unit upon power-up of the transmission. If a recent request, i.e. control command for preparing the transmission for disassembly can be detected a calibration of the position detection sensor is performed.
The disclosure also concerns automatic transmission arranged to perform the methods described above, as well as a computer program comprising program code means for performing all the steps of the methods when said program is run on a computer, a computer program product comprising program code means stored on a computer readable medium for performing all the steps of the methods when said program product is run on a computer, and a computer system for implementing the described methods.
Further advantages are achieved by implementing one or several of the features of the dependent claims.
According to an aspect of the disclosure, the method further comprises registering the position of at least two gearshift actuators at power-up of the transmission, and performing a calibration of the associated position detection sensor if each registered position of the at least two gearshift actuators is outside a predetermined expected position range or if each registered position of the at least two gearshift actuators is within a predetermined abnormal position range. This method results in a decreased risk for performing a calibration due to measurement errors of the position detection sensor. The position detection sensors all involve a certain level of measurement error. For example, the output signal of the sensors varies with temperature. Moreover, the output signal of sensor more or less accurately represents the true condition of the measured object, which accuracy often is defined in terms of for example +/− a certain percentage. If the decision to perform a calibration is based on the output signal of two position detection sensors instead of a single sensor, the likelihood of an unnecessary calibration is reduced due to the reduced likelihood that the output signal of both sensors simultaneously involves a sufficiently large measurement error.
The method according to the disclosure is usable for a variety of different automatic transmissions arranged to shift gears using actuators.